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Too bad they didn't make a car for the D engine, then it might be cheaper than a limited production "aircraft" engine - Maybe that don't count now - Continental, Lycoming and Bombardier have made a Jillion engines, and they still cost too much!

A VW or Soob with redrive may still be the cheapest 4-stroke engine for small homebuilts.

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Ed, the Yamaha engine Jim shows in the first post on this thread is a good example of a mass produced engine that could be a good fit for small homebuilts.

I've been interested in this engine ever since I saw a post about it a year ago. There is a Kitfox not too far from me that has one, and it's reported to have amazing takeoff performance. I haven't gotten a chance to go see it, but I plan to. Now that this adaptor is being offered for the Rotax gearbox, I wonder if more people will try it. Here is a link to the barnstormers ad (I have no connection).

Anyone know of any drawbacks with this engine? As Leni said, Gyro guys have been using them for a while. There is a really long thread on one of the rotorywing forums about various user experiences. I'm surprised it hasn't been more popular based on the weight and power.

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No argument. The Subaru is a good engine. Many have had success with them. This is just another option. I think it's a little more comparable to the Rotax in the power to weight category. I have to admit it sounds a little too good to be true though. Read this thread for some more info:

Sounds like most guys just buy a used snowmobile (sorry, that's what we call them in Oregon), and take out the motor. Early in that thread they say they can be had for about $3000, but that was in 2008. Not sure what they cost now. Maybe $3000 + $1500 + $2500 = $7000 ?? That's just using your number on the gearbox. I don't really know what they cost.

Also, if I bought a used Subaru for $2500, I know I'd be putting quite a bit more money into it before I was comfortable flying behind it. Like I said, nothing against the Subaru. Just another option.

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That is A great engine, but to make full power I think it is around 9000 rpm so it has a built in gear reduction for the snowmobile clutch and then you have to add another gearbox seems like extra weight to me. Another down fall is when that engine overheats for just a split second the computer instantly puts it in limp mode, If they can reprogram that it will be a killer engine I think. My dad has a turboed three cylinder in his Nitro and it moves.

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That is A great engine, but to make full power I think it is around 9000 rpm so it has a built in gear reduction for the snowmobile clutch and then you have to add another gearbox seems like extra weight to me. Another down fall is when that engine overheats for just a split second the computer instantly puts it in limp mode, If they can reprogram that it will be a killer engine I think. My dad has a turboed three cylinder in his Nitro and it moves.

TJay,

The original EA-81 Subaru (I call it Soob) car engines were hooked up to a computer, and also had a "limp-home" feature. I think it may have been around 3000 rpm, (that's engine speed - not prop speed), but would have to go back into my old books to be certain on that speed.

When adapted to aircraft, some rotary-craft continued to use the computer, but that was soon bypassed and a direct ignition system was used - some made dual points for it, and some even used dual coils. They sold heads in Australia with dual sparkplugs, which, IMO, were not needed.

They no longer had the limp-home feature connected, and it worked fine.

EdMO

Edited 11 Sep 2015 by Ed In Missouri

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Yamaha Genesis 4 cyl engines (YG4 is what we call them) weigh 118 lbs FI and 125 lbs with the carbs. The latter has both liquid and electric carb heat. You only need the liquid heating, I recommend removing the electric heating wiring. Installed weight on my projects to date for the carb engine is 165 lbs with dual steel mufflers and 4 into two SS exhaust, including oil tank, electronics, radiator, factory intake silencer, all hoses and connections. HP is 150 and 143, respectively. The FI gets a bump in HP from a more aggressive cam profile. With the last install, when we remove the mufflers we see a 100 RPM uptick in RPM, not enough to sweat so I know we got the back pressures right and very little restrictive flow.

Fuel burn is 3 GPH min, and with two souls in my gyroplane, about 1050 TOW we burn 6 GPH. Normal cruise with pilot alone in a gyroplane is 4-4.5 GPH.

I don't know Soobs, but have been told by those that do that they weigh up to 320 lbs installed for the biggest of them, the 2.5L that reportedly makes 160HP. That's the only Soob that is in the same power class as the Yamaha 4. Difference here is enormous, like dragging your 155 lbs mother-in-law around with you on every flight. I have second hand knowledge of innumerable Soobie engine outs. One CFI I know personally here in Georgia has had several on a single gyroplane. I can't for the life of me imagine anyone wanting a Subaru anymore. If you have an aircraft with a Soob on it and it is trouble-free, hey good for you, enjoy your flying. They were a good option ten years ago, but with the Yamaha options available today it is outdated and anyone looking for a fresh start should not be considering anything but Yamaha as an alternative to the insanely expensive Rotax. When you consider that a Rotax 914UL isn't even a certified engine, weighs a bit more than the Yamaha, costs $30,000 new and at least $15,000 used yet only puts out a meager 115 HP for 4 minutes max, why even go there other than you feel better about having a redundant ignition. That's it, in a nutshell. I have yet to hear of a single YG4 engine out and we have been running Yamahas on gyroplanes for nearly ten years now.

I had a YG4 carb heat wire break off from its connector (my installation error) and go to ground, frying the voltage regulator. When the battery went below 12v the ECU and the factory Yamaha tach/multi-function display (MFD) died. I didn't even realize this until I glanced down at my panel for a quick routine check. I turned back to the airport, landed, engine never missed a beat, never lost RPM. That's because the plugs are hard-wired to the mag and continue to fire even when you disco the ECU! Each plug has it's own coil, recessed fully in a deep well in the head. What are the chances of losing more than one coil or plug at the same time? With even two plugs/coils lost this engine will still have plenty of power to get you on the ground safely, most likely at a proper airport.